Silver is used extensively for industrial purposes owing to its exceptional properties (e.g., high electrical and thermal conductivity, malleability, ductility, and its resistance to corrosion). To illustrate, common uses for, or products incorporating, silver or silver compounds include photographic materials, electroplating, electrical conductors, dental alloys, solder and brazing alloys, paints, jewelry, coins, mirror production, antibacterial agents, and water purification.
With such extensive use, not only is there a tremendous consumption of metallic silver, there is also a large production of silver-containing wastewater. The discharge of silver, and other metals, is a concern of both government regulatory agencies and the industries that use silver in their manufacturing processes. In fact, silver is a regulated material. Consequently, there are limits to the amount of silver that can be present in streams that are discharged into normal industrial sewage systems or the like. In addition, supplies of silver raw materials are dwindling because of their scarcity, while demands for silver in industries are still increasing. Therefore, recovery of silver from industrial wastewaters is of interest, for both water resource protection and silver reclamation.
To date, many methods have been developed to recover silver from industrial wastewaters, including chemical reduction, membrane filtration, ion exchange adsorption and electrochemical methods. Each of the methods has distinct advantages and disadvantages in practical applications. For example, existing methods based on chemical reduction offer simplicity, low manufacturing cost, fast reaction times, and efficient scale-up efficiency/ease for large scale wastewater treatment. On the other hand, the reducing agents employed for such methods are frequently toxic and/or carcinogenic, and can cause safety and health problems when implemented in high volumes.
There accordingly remains a need for improved technologies that can be used to recover silver from industrial wastewaters. It would be particularly advantageous if these methods provided minimal health and safety impact while simultaneously maintaining, or improving upon, the positive attributes of existing silver recovery techniques. It is to the provision of such technologies that the present disclosure is directed.